/*
    Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

    For example:
    Given the below binary tree and sum = 22,
                  5
                 / \
                4   8
               /   / \
              11  13  4
             /  \      \
            7    2      1
    return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.
*/

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

// Recursion, time: O(n)
public class Solution {
    public boolean hasPathSum(TreeNode root, int sum) {
        if (root == null)   return false;
        if (root.left==null && root.right==null)    return sum == root.val;
        return hasPathSum(root.left, sum- root.val) || hasPathSum(root.right, sum-root.val);
    }
}